An X-ray detection is widely used in fields such as medical treatment, safety inspection, non-intrusive examination and scientific research. A typical X-ray detection technique is the X-ray digital radiography (DR) detection technique which is emerged in the late 1990s. A flat panel detector is arranged in an X-ray DR system, and each pixel size of the flat panel detector may be less than 0.1 mm, so that the flat panel detector may capture an image that has good quality and high definition comparable with film photography, while the flat panel detector overcomes the shortcomings of the film photography and facilitates the digital image processing.
Based on the digital conversion modes, digital X-ray flat panel detectors may be classified into two categories: a direct DR X-ray flat panel detector and an indirect DR X-ray flat panel detector. The indirect DR X-ray flat panel detector includes an X-ray conversion layer formed by a scintillator (for example, cesium iodide) or a fluorophor (for example, gadolinium oxysulfide), photodiodes, thin film transistors (TFTs), pixel units, signal amplification units and signal reading units. In such indirect DR X-ray flat panel detector, the X-ray may be converted into an electrical signal by a scintillator layer or a fluorophor layer after the scintillator layer or the fluorophor layer is exposed by the X-ray, the electrical signal of each pixel unit is read out and converted into a digital signal by a TFT array, and the digital signal is transmitted to a digital image processing computer system to be synthesized into an X-ray image.
The electrical signal converted by the photodiode is collected mainly by drift movement which is driven by a build-in electric field; and the greater a strength of the build-in electric field is, the faster a speed of collecting the charges is. The strength of the build-in electric field of the photodiode depends on a doping concentration of boron atoms and phosphorus atoms in P-type and N-type materials of the photodiode. However, the doping concentration of boron atoms and phosphorus atoms is limited by a saturation concentration; and properties of the material deteriorate when the saturation concentration is exceeded. Furthermore, amorphous compositions in amorphous silicon material have defects such as dangling bonds, and thus the charges may be captured by the defects when the charges are collected, so that output efficiency is lowered, and both detection efficiency and sensitivity of the X-ray detector are reduced.